Particularly with respect to load carrying vehicles, such as trucks, common carriers and buses, their great weight and hence great inertia give rise to problems in their operation. The vehicles are both braked, which leads to their immobilization, and they are slowed or decelerated, which consists in diminishing their velocity.
For braking purposes, vehicles are equipped with drum or disc brakes. Brake operation is based on friction produced by rubbing of a brake shoe or block against a drum or disc. The material of the drum or disc is a casting of iron having specific characteristics. The lining of the brake shoe is an agglomerate made from an asbestos base and special formulations depending on the case. The absorbed energy caused by braking is transformed into heat. This raises the temperature of the brake shoe lining and of the brake drum or disc. The heat is subsequently dissipated by a current of air. The permissible temperature rise of the lining and drum or disc has an upper limit, because it can lead to changes in their structures, and can even damage these elements. Furthermore, the coefficient of friction of the brake drops substantially, reducing the braking capacity when a temperature of approximately 350.degree.-400.degree. C. is exceeded. With infrequent use of the brake, there will be time between brakings for dissipation of heat, and the temperature of the brake components will not harmfully rise. But, if the brake is used very frequently, or is operated for long periods, there is a risk of incapacitating the brake with the resultant possibility of an accident.
These drawbacks of brakes have led to the creation of speed reducers which diminish, or at least do not increase, the speed of the vehicle, although they do not serve to immobilize the vehicle, as this is still the function of conventional brakes. These speed reducers are not damaged even when used frequently or over prolonged periods. The most common application of speed reducers involves their insertion in the transmissions of heavy vehicles. The most common type of speed reducer is an eddy current brake and operates electromagnetically, in which braking action originates in the Foucault currents stemming from the resistance as a magnetizable material drive or flywheel moves within the magnetic field created as a direct current passes through the magnet coils of the stator of the device. The braking force is proportional to the space or air-gap existing between the rotor or flywheel and the poles of the stator coil. This space is typically on the order of 1 to 1.5 mm. Moreover, the flywheels have an outside diameter in the range of 300 mm. to 500 mm., and are subjected to velocities which in modern transmissions exceed 2,000 rpm. All of this, combined with the high braking forces produced, leads to the use of speed reducers of a weight of around 200 kg. This requires rigidity in the placement of the stator relative to the movement of the flywheels, and requires great precision in the positioning or gauging of the stator relative to the flywheels.
At the present time, speed reducers are often placed between the gearbox and the rear axle, generally the driving axle. This makes it necessary to attach the speed reducer to the fixed chassis, while the rear shaft floats with respect to the chassis. Therefore, the speed reducer will tend to float with respect to the rear shaft, which implies lack of rigidity of installation. In the case of short transmissions, there is practically no space in which to place the speed reducer.
Alternatively, the speed reducer is suspended from the chassis. The chassis must have in its interior the central body which accommodates the shaft and the bearing supporting the movement of the flywheels, wherein the bearing shaft assembly is included between the flywheels. Such placement leads to problems of cooling, limited space for lubricant, difficulties in applying lubrication due to problems of access, and difficulties of insulating the elements magnetically against the influence of the magnetic field on the bearings, which reduces their useful lives.